Chemistry_Grade_10-12 (1).pdf

252 chapter 13 quantitative aspects of chemical

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CHAPTER 13. QUANTITATIVE ASPECTS OF CHEMICAL CHANGE - GRADE 11 13.9 A limiting reagent is the chemical that is used up first in a reaction, and which therefore determines how far the reaction will go before it has to stop. An excess reagent is a chemical that is in greater quantity than the limiting reagent in the reaction. Once the reaction is complete, there will still be some of this chemical that has not been used up. Exercise: Summary Exercise 1. Write only the word/term for each of the following descriptions: (a) the mass of one mole of a substance (b) the number of particles in one mole of a substance 2. Multiple choice: Choose the one correct answer from those given. A 5 g of magnesium chloride is formed as the product of a chemical reaction. Select the true statement from the answers below: i. 0.08 moles of magnesium chloride are formed in the reaction ii. the number of atoms of Cl in the product is approximately 0.6023 × 10 23 iii. the number of atoms of Mg is 0.05 iv. the atomic ratio of Mg atoms to Cl atoms in the product is 1:1 B 2 moles of oxygen gas react with hydrogen. What is the mass of oxygen in the reactants? i. 32 g ii. 0.125 g iii. 64 g iv. 0.063 g C In the compound potassium sulphate (K 2 SO 4 ), oxygen makes up x% of the mass of the compound. x = ... i. 36.8 ii. 9.2 iii. 4 iv. 18.3 D The molarity of a 150 cm 3 solution, containing 5 g of NaCl is... i. 0.09 M ii. 5.7 × 10 4 M iii. 0.57 M iv. 0.03 M 3. 300 cm 3 of a 0.1 mol.dm 3 solution of sulfuric acid is added to 200 cm 3 of a 0.5 mol.dm 3 solution of sodium hydroxide. a Write down a balanced equation for the reaction which takes place when these two solutions are mixed. b Calculate the number of moles of sulfuric acid which were added to the sodium hydroxide solution. c Is the number of moles of sulfuric acid enough to fully neutralise the sodium hydroxide solution? Support your answer by showing all relevant calcula- tions. (IEB Paper 2 2004) 4. Ozone (O 3 ) reacts with nitrogen monoxide gas (NO) to produce NO 2 gas. The NO gas forms largely as a result of emissions from the exhausts of motor vehicles and from certain jet planes. The NO 2 gas also causes the brown smog (smoke and fog), which is seen over most urban areas. This gas is also harmful to humans, as it causes breathing (respiratory) problems. The following equation indicates the reaction between ozone and nitrogen monoxide: 253
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13.9 CHAPTER 13. QUANTITATIVE ASPECTS OF CHEMICAL CHANGE - GRADE 11 O 3 ( g ) + NO ( g ) O 2 ( g ) + NO 2 ( g ) In one such reaction 0.74 g of O 3 reacts with 0.67 g NO. a Calculate the number of moles of O 3 and of NO present at the start of the reaction. b Identify the limiting reagent in the reaction and justify your answer. c Calculate the mass of NO 2 produced from the reaction. (DoE Exemplar Paper 2, 2007) 5. A learner is asked to make 200 cm 3 of sodium hydroxide (NaOH) solution of concentration 0.5 mol.dm 3 .
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